The present invention relates to a hose with corrugated metal tube which is suitable for fuel conveying hose for automobiles, refrigerant conveying hose or any other fluid conveying hose, and more particularly to a hose with corrugated metal tube including characteristic structure of an axial end portion thereof.
Typical rubber hoses, for example, made of blended product of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC blend) which is excellent in resistance to gasoline permeability, have been used for conveying fuel for automobiles or the like in view of their high vibration-absorbability, easy assembling or the like. However, for the purpose of global environment protection, the regulations have been recently tighten against permeation of fuel for automobiles or the like, and are anticipated to be further tighten in the future. Further, hoses are demanded to meet the requirements to convey highly permeable fluid such as, hydrogen gas used in fuel cells or carbon dioxide (CO2) refrigerant. Then it is anticipated difficult to satisfy the future requirements with hoses made only of organic materials such as rubber or resin.
Accordingly, it is currently considered to adapt a hose having a corrugated metal tube for inner layer as future hose of low fluid permeability because such a hose is expected to have an extremely high fluid impermeability.
As for a hose with corrugated metal tube, such hoses as disclosed in the-following patent documents, 1, 2 and 3 are known.
In case of these hoses with corrugated metal tube, even if adapted for hydrogen gas used for fuel cells, a corrugated metal tube in or as an inner layer reduces gas permeation to zero, i.e., completely eliminates permeation of gas.    1. JP, A, 2001-182872    2. US20020007860A1    3. JP, U, 51-150511
And, FIG. 5 shows a hose with corrugated metal tube of this type which is invented by the inventors of the present invention and helpful for better understanding of the present invention. In FIG. 5, a numeral reference 200 indicates a hose body. The hose body 200 is formed multi-layered. The multi-layered construction has inner layer including a corrugated metal tube 202 of innermost layer and outer layer which circumscribe a radial outer side of the inner layer and includes inner elastic layer 204, reinforced layer 206 and outer elastic layer 208.
A numeral reference 210 indicates a socket fitting fitted on an outer periphery of the hose body 200 on an axial or longitudinal end portion, or on one axial or longitudinal end portion of the hose body 200. The socket fitting 210 is compressed or swaged radially inwardly at three axially spaced points P1, P2 and P3 thereof or on a cylindrical portion of the socket fitting 210. And thereby the socket fitting 210 and a connecting pipe 212 are fixedly secured to one axial or longitudinal end portion of the hose body 200 so as to clamp one axial or longitudinal end portion of the hose body 200 therebetween from inner and outer sides thereof.
Meanwhile, as shown in FIG. 6, in such hose with corrugated metal tube, the corrugated metal tube 202 tends to expand or elongate in an axial or longitudinal direction when an internal pressure is exerted thereto. Therefore, such hose with corrugated metal tube inherently involves a fear that when an internal pressure is exerted thereto repeatedly at pulse intervals, the corrugated metal tube 202 overall repeatedly oscillatingly elongates or expands and contracts in a longitudinal direction, and consequently repeated longitudinal deformation thereof causes a fatigue crack or crack in the corrugated metal tube 202 in any portions thereof. More specifically, it is predicted that the corrugated metal tube 202 is strongly restrained from moving on the last swaged point P3, a stress is likely concentrated in a position corresponding to the last swaged point P3, and consequently the corrugated metal tube 202 is likely subject to fatigue crack or break at the last swaged point P3.
However the inventors of the present invention actually conducted a impulse test or repeated pressurizing test to exert internal pressure repeatedly to this hose with corrugated metal tube and found the fact that the corrugated metal tube 202 is cracked or broken generally at a certain distance axially away from the last swaged point P3 of the socket fitting 210. More specifically, the inventors found the fact that the corrugated metal tube 202 is broken about at 7.0 mm axially away from the last swaged point P3.
The reason is estimated that a portion of the hose body 200 inside of the socket fitting 210 is strongly compressed radially inwardly at the last swaged point P3 when compressing or swaging the socket fitting 210 radially inwardly, and the compressed portion of the hose body 200 is partly extruded or squeezed out rearwardly (toward the right hand in FIG. 5) as shown by a right-hand arrow in FIG. 5.
The above are described with reference to a hose for conveying hydrogen gas used in a fuel cell as example. The similar problems are anticipated in common to any hoses. For example, it may be the case that a hose with corrugated metal tube is employed to convey fuel such as gasoline for the purpose to deal with gasoline or the like permeating to an air or for high temperature and high pressure application due to high output power of equipment, where low permeability property is severely regulated. Also, it may be the case that a hose with corrugated metal tube is employed to covey carbon dioxide (CO2) as refrigerant fluid, which is low in amount of particles just like hydrogen and is highly permeable. Further, it may be any other case that a hose with corrugated metal tube is applied in fields under severe regulations against gas permeation.
It is an object of the present invention to provide a hose with corrugated metal tube to settle the problems described above.